Recent combined clinical and microbiological/physico-chemical studies within the Forsyth Specialized Caries Center suggest strongly that a segment of the microflora which we have termed the 'low-pH' non-mutans streptococci ('low-pH non-MS) may play a significant role in the caries process and that the levels of these organisms are correlated with a battery of plaque parameters which we have termed putative, pathognomonic, physico-chemical plaque characteristics (PPPC). The purpose of the proposed effort is to implicate the 'low-pH non-MS' in the process of ongoing human caries activity, to relate these organisms (as well as mutans streptococci and some selected weakly indicted organisms) to PPPC and diet, and finally to model disease incidence by way of logistic regression analysis. Four hundred at-risk adults including appropriate numbers of women and minorities, 65-75 years of age, will be recruited and seen at baseline, 6, 12, and 18 months. A thorough clinical examination (except for radiographs) will be carried out at each time point, plaque will be harvested from every sound, susceptible, exposed root surface, a dietary history will be taken and saliva will be collected. Pooled plaque as well as plaque from each exposed root site will be analyzed for the microorganisms cited above and for PPPC. The salivary collections will yield flow rates. The large-scale microbial assay work will be made possible by the development and application of DNA probes. Cross-sectional analyses will relate prevalence and levels of root surface caries to target organisms, PPPC and cariogenicity of diet. Interrelations among these risk factors will be evaluated. Longitudinally, newly-developing lesions will be compared to appropriate control surfaces for pre-disease microbial profiles and PPPC. At the termination of the longitudinal study, root caries incidence will be modeled primarily in terms of pertinent clinical parameters, microbial and PPPC profiles, diet, and salivary flow rate and some peripheral variables. This study has the potential for implicating a new group of organisms in the caries process, fully characterizing the PPPC in relation to disease, relating microflora, PPPC, and diet, while producing the most explanative models of the caries process to date. In addition, it will entail the first extensive application of probe technology in caries research and produce a comprehensive, presently unavailable collection of probes for potential cariogenic pathogens.